1. Field of the Invention
The present invention is directed to an improved powder press assembly capable of subjecting the frame and die set to only compressive forces while accurately maintaining the dimensions of compactive parts and more particularly to a press assembly having mechanical stops in the upper and lower ram assemblies, a multi-function push rod assembly and a dual hydraulic system including a bypass valve in the main pressure cylinder.
2. Description of the Prior Art
A number of companies have manufactured compacting powder presses of up to 1,000 tons capacity and in special applications have created presses capable of 10,000 tons and greater force. Press manufacturers have recognized the advantages of accurately forming complex shaped parts from powder with a compacting press assembly to eliminate expensive machining and labor costs. These parts have been found useful in almost every major industry. A number of different materials can be utilized in a powder compacting press, for example, various forms of metal powders, aluminum, carbides, carbons, ceramics, stainless steel, ferrites, glass, fluorocarbon resins, etc.
As can be readily appreciated by a person skilled in this industry, the cost of these high pressure compacting presses represent a large capital investment. Generally, most of the presses do not have the ability to press exactly to both an exact part height as well as to an exact density. Frequently, parts are relatively complex or have multi-levels with counterbores, through holes, flanges, tapers or hubs and accordingly, require a plurality of die sets to interact to produce the final shape of the part. Because of this complex and sometimes extensive surface area, considerable friction can be generated between the formed part and the die sets and quite frequently the ejection capacity of a compacting press must be 50% or greater of the pressing capacity. Most commercial mechanical and hydraulic presses do not have the capability to create ejection forces as great as their compression forces particularly throughout the entire ejection stroke.
A number of compacting presses utilize a mechanical power source as can be seen in the Assmann U.S. Pat. No. 3,172,182 or a combination of hydraulic and mechanical power. In the ejection mode, the die set members can be subjected to tension forces and require appropriate heavier tooling component design. The prior art has further suggested various forms of powder metallurgic presses utilizing auxiliary hydraulic systems and controlled stops for positioning such as shown in the Bush U.S. Pat. No. 3,078,540 and the Walchhuetter U.S. Pat. No. 3,830,615.
The Cremer U.S. Pat. No. 2,336,982 is cited of interest to disclose a unidirectional compressive force stroke during both pressing and ejection. The Belden U.S. Pat. No. 2,831,212 is cited to disclose an arrangement of a prepressing die control. The Hermes U.S. Pat. No. 3,587,136; Priebe U.S. Pat. No. 3,777,539 and Schmoll et al U.S. Pat. No. 3,847,008 are cited of general interest.
There is a need in the compacting press industry for a superior compacting press capable of generating repeatable close part height tolerance with equal compacting and ejection force for all tonnage ranges. It is also desirous in the compacting press industry to subject the tooling members only to compression while maintaining an ability to press to positive stops.